Rheostat and heater



(No Model.)

B. G. MITCHELL.

RHEOSTAT AND HEATER. No 528,907. Patented Nov. 6, 1894.

WITNESSES: INVENTOR @fm $4" 72% a UNITED STATES PATENT OFFICE.

ROBERT C. MITCHELL, OF NEWV YORK, ASSIGNOR OF ONE-HALF TO HENRY W. VAIL,OF BROOKLYN, NEW YORK.

RH EOSTAT AND HEATER.

BPEGIFIGATION forming part of Letters Patent No. 528,907, dated November6, 1 894.

Application filed January 894- Serial No. 497.209. (llo model.)

To all whom it may concern.-

Be it known that 1, ROBERT C. MITCHELL, of the city of New York, countyand State of New York, have invented certain new and useful Improvementsin Rheostats and Heaters, of which the following is a specification.

My invention consists in the novel mechanism hereinafter fullydescribed.

The object of my invention is to provide in a rheostat and heater, apositive means of insulating the resistance wire from the base, whetherthe said base be flat or curved.

My invention is illustrated by the accompanying drawings, in whichFigure 1, is a plan view of a flat rheostat or heater, sections of theseveral layers being broken off from one corner thereof for the purposeof revealing the construction. Fig. 2,is an enlarged transversecross-section of a portion of the mechanism.

Similar letters refer to similar parts in both views.

My invention is of particular value as an electric heater for the reasonthat in all such devices the base plate is formed from steel or iron,and it is therefore particularly important that a perfect insulation beinterposed be tween the said plate and the resistance wire.

It is also important that this insulation be as thin as possible so thatthe source of the heat, the hot resistance, can lie very closely to thebase plate of the heater, in which event the heat from the resistancewire will have very little to penetrate before acting directly on theheater plate. This latter feature is a recognized factor of importance.

A is a base or support made from any suitable material, and may be flator cylindrical or of any desired shape.

B is a sheet of insulating material, by preference mica. By the use ofmica are gained several points. Firstit is an admirable nonconductor,and second, it is non-fusible, does not get soft and is not seriouslyaffected by heat. It is obvious that any other substance, that possessessubstantially these properties, may be substituted.

D D are perforations formed in the sheet B. These perforations may be ofany desired shape or number.

E is a resistance wire shaped in any desirable manner.

The sheet of insulating material B is placed upon the base A and thenthe resistance wire E is placed upon the sheet 13. A suitable cover ofinsulating substance F is then placed over the sheetB and resistancewire E and allowed to run, or is forced, down into and through theperforations D D until it contacts with the plate A. By preference Imake use of a cohesive substance such as enamel, or lava or the like.The apparatus is then placed in a furnace and the insulating substanceis baked so as to harden it and thus unite the several parts into onesolid body. By preference a considerable part of the sheet Bisperforated so that a large holding surface on the baseA is exposed'tothe covering F. Where lava or other porous insulation is used 1preferably treat its exposed surface toa coating of waterproofingsubstance G, for instance enamel, that is not seriously affected byheat.

It is obvious that the perforations may extend entirely across the widthof the sheetB thereby cutting it into several sheets to lie between theplate A and the resistance E.

If the base A is cylindrical the sheet B may be Wrapped around it.

The particular advantage of placing an insulating material, that doesnot become soft by heat, between the base and the resistance wire is,that there is no possibility of the resistance wire being pressedthrough this sheet of insulation against the plate, should the surfaceof the insulation F be rolled or otherwise presssed, thereby causing aground or shortcircuit.

Having thus described my invention, what I claim, and desire to secureby Letters Patent, is-

1. The combination of the base A, the perforated insulation B, theresistance E, with the covering F, substantially as described.

2. The combination of the base A, the resistance E, having interposedbetween the plate A. and resistance E, the perforated insulation B ofmica with a covering of insu- B interposed between the base A and wire Elating substance F enveloping the resistance with a covering ofinsulating substance Fsub- IO E and contacting with the base A throughthe stantially as and for the purpose specified. perforations D Dsubstantially as and for the ROBERT C. MITCHELL. 5 purpose specified.

3. The combination in a heater, of a metal Witnesses. base A, theresistance wire E with the perfo- JOHN KENNY, J r.,

rated sheet or sheets of non-fusible insulation H. B. BROWNELL.

